1. Field of the Invention
The present invention relates to a plasma-processing apparatus and more particularly, an apparatus for processing a substrate such as the semiconductor wafer with plasma excited by electron beam.
2. Description of the Related Art
In recent years, as semiconductor devices are more finely structured to have a higher capacity, a more finely process must be applied to semiconductor wafers in the course of plasma-etching the wafers. It is needed for this purpose that process gas is more efficiently made into plasma while reducing the pressure in the process chamber of the plasma etching apparatus to a greater extent. As one of the plasma etching apparatuses by which this plasma process can be achieved, there has been well-known the plasma etching apparatus of the electron beam exciting type wherein electrons are drawn out of sub-plasma, accelerated and introduced into the process chamber to excite the process gas into main plasma with which the semiconductor water is etched.
Published Unexamined Japanese Patent Application No. 1-105539 discloses an apparatus of this kind in which electron beam is diffused by a deflecting electrode. Published Unexamined Japanese Patent Application No. 1-15540 discloses an apparatus of this kind in which magnetic field canceling means is provided to diffuse electron beam. Published Unexamined Japanese Patent Application No. 63-190299 discloses an apparatus of this kind in which a pair of electrodes are fixed through a spacer. Published Unexamined Japanese Patent Application No. 64-53422 discloses an apparatus of this kind in which second means is provided to make etching gas into plasma by using other plasma generated by first means. Published unexamined Japanese Patent Application No. 59-27499 discloses an apparatus of this kind in which plasma density is made uniform in such a way that rectangle-shaped permanent magnets are arranged on both sides of electron beam introduced into the process chamber to compress and spread plasma region flat like a sheet by their lines of magnetic force.
In the plasma etching apparatus wherein the semiconductor wafer is positioned perpendicular to the direction in which exciting electrons are shot, the etching process can be achieved by high energy ions. As semiconductor devices are more and more finely structured these days, however, oxide, resist and interconnecting films, for example, formed on the wafer become thinner. In the case of the above-mentioned plasma etching apparatuses, therefore, the semiconductor wafer is contaminated by high energy ions and its insulating and resist films are also broken and inflamed by them. In the case where the wafer is arranged perpendicular to the electron shooting direction, the density of plasma becomes higher as it comes nearer to the center of the wafer. This makes it difficult to apply uniform process to the whole surface of the wafer.
In a case where the processed surface of the substrate is positioned parallel to the electron shooting direction, it is needed that a sheet-like plasma region is formed to have a uniform density relative to the processed surface of the substrate. According to the conventional method of forming the sheet-like plasma region, column-like plasma generated by discharge in magnetic field is compressed and spread flat by a pair of rectangle-shaped permanent magnets. The sheet-like plasma region can be formed to have certain thickness and area according to this conventional method. However, the sheet-like plasma region thus formed leaves beam-like components around its axis. This makes it impossible to obtain a plasma region high and uniform in density all over a larger area. The conventional method of forming the sheet-like plasma region, therefore, is not suitable for uniformly processing such a matter as the semiconductor wafer which has a large area.
The above-mentioned problems are common to the semiconductor wafer plasma processing apparatuses including the plasma etching CVD and sputtering apparatuses which use various kinds of system of generating plasma.